Conditional access (CA) and Digital Rights Management (DRM) systems for digital video transmissions are widely used to secure commercial television services. Such systems typically use encryption to secure media transmission to digital client devices, such as a set-top box, mobile device or PC. The CA or DRM system implements the controlled distribution of the decryption keys to authorized receivers only. The keys are typically required for content playback and the keys are often secured against unauthorized discovery by secrets embedded in and protected by the client device.
A conditional access (CA) system provides access to digital broadcast content for authorized individuals and can be implemented as discussed below.
A CA server typically includes head-end equipment that is connected to multiplexing and scrambling system of Transport Streams (TS) and is configured to manage the process of encryption TV program and data, injecting service information and customer management. A CA system typically includes the following components for content protection.
A conditional access (CA) server includes a Control Word Generator (CWG) that generates CWs (Control Words) that are used by the scrambler to scramble and thereby secure the content. Encryption is often used to protect the control word (CW) during transmission to the client receiver. The control word (CW) is typically encrypted and delivered via an Entitlement Control Message (ECM). Typically, only the authorized subscriber's equipment is permitted to decrypt the control word (CW). The entitlement or authority as well as the keys to decrypt the CW in the ECM is sent to the receiver in the form of an Entitlement Management Message (EMM).
A Multiplexer/Scrambler provides the scrambling of audio/video streams using a CW control word. The multiplexer (MUX) accepts Program Streams (PS), Entitlement Management Message (EMM), Entitlement Control Message (ECM) and Event Info Scheduler (EIS) information. The multiplexer (MUX) performs time multiplexing of input data and outputs an MPEG-2 transport stream.
The control word (CW) is typically sent to the receiver in encrypted form within an entitlement control message (ECM). The CW is valid for a particular crypto-period (CP), which is typically 10 seconds long. The ECMs are typically repeated (e.g., 10 times per second) so that the set-top boxes (STBs) are able to quickly start descrambling after changing channels.
Additionally, the CA or DRM system also often implements control and/or authentication mechanisms during playback that manage how the content may be processed, used, and secured. Examples are controls of allowed outputs (e.g., DHCP) and digital watermarking.